At least 126 million women give birth every year worldwide. Over 20 million of them experience a pregnancy related complication or illness. For example, hypertensive disorders such as pre-eclampsia affect more than 10% of all pregnancies and are a leading cause of maternal death. Adequate prenatal health care decreases the chances that such complications and illnesses will go unnoticed. In many countries, screening methods for determining the risk of prenatal complications and/or fetal abnormalities have become routine to aid in treating and advising pregnant women. For example, throughout Europe, the United States and some regions in Asia, health care providers commonly screen for chromosomal abnormalities in the fetus using biochemical markers present in maternal blood. Such screening is helpful for identifying women who have sufficiently high risk to justify further diagnostic testing, which can be invasive and carry risk to the fetus. Maternal blood and other fluids also contain biochemical markers that can be used to detect pregnancy related illnesses of the woman. Even so, currently no routine screens have been adopted for early detection of pre-eclampsia using maternal samples. Thus, there exists the need to develop accurate screening methods for prenatal complications and/or fetal abnormalities.